The present invention relates to a device for automatic spray application of paint through a spray nozzle. The device comprises a container containing paint and arranged in the immediate proximity of the spray nozzle. The container is connected to the spray nozzle through a conduit for supplying paint thereto for spray application. The device further includes pressing means adapted to press the paint out of the container and through the conduit to the nozzle through a pressurized medium.
Such a device may have different fields of use, but for illustrating, but not in any way restricting the invention, the use of such a device for painting objects, such as vehicle bodies, through a spray painting robot will hereinafter primarily be discussed. Notwithstanding, the invention also comprises devices in the form of so called painting machines. xe2x80x9cPaintxe2x80x9d is here to be given a broad meaning and comprises all types of paints suited for spray application.
It is often desired to place such a container containing paint in spray application robots close to the spray nozzle to avoid long conduits between the source of paint and the spray nozzle. This is done primarily to avoid a great waste of paint when color is changed, but also to facilitate cleaning of such conduits and avoid having long conduits impede the ability to move the robot or otherwise constitute obstacles. However, a problem arises when the container is arranged close to the spray nozzle, if the container and the robot arm carrying the spray nozzle are moved so that the container is turned or tilted. The paint present in the container will, upon such movements of the container, assume a new position in the container through gravitation and may perhaps not be reachable by the conduit in this position, so that it will not be possible to spray paint out through the spray nozzle in certain positions of the robot arm, and thereby the container. Similarly, it may not be possible to efficiently discharge all the paint from the container should this be desired. Rather, the problem of supplying the spray nozzle with paint will instead increase with a decreasing content of paint in the container.
A solution to this problem is presented in FR 2 635 990, which consists of arranging a member for mechanically dividing the container inside the container for separating the paint and the pressurized medium, such as compressed air, in which this member is formed by a piston or a flexible membrane. However, an arrangement of such a membrane or piston in the container requires control means that are unnecessarily complicated and makes the construction of the container unnecessarily costly.
The object of the present invention is to provide a device of the type mentioned in the introduction, which solves the problem discussed above in a simpler, more advantageous and less costly way than has been achieved through the device according to the French publication mentioned above.
This object is obtained, according to the invention, by arranging the container to be rotatable and providing the device with members adapted to drive the container to rotate, for pressing paint contained therein outwardly towards a region of the periphery thereof. Further, the conduit has an opening in the peripheral region, and that the pressing means are adapted to establish an overpressure of the pressurized medium in the container for pressing paint out through the opening to the spray nozzle.
Thus, regardless of its positioning in the interior of the container, it may always be ensured that paint contained in the container is present where the conduit terminates in the container. Thus, paint may be supplied to the spray nozzle as long as there is any paint left in the container. This is achieved completely without any requirement of any membrane or piston inside the container. It is a matter of course that the driving member has to drive the container to rotate with such a speed that xe2x80x9cthe centrifugal forcexe2x80x9d keeps the paint against the periphery of the container. It is also within the scope of the invention that the driving member does not have to drive the container to rotate continuously, but this capability is present and utilized when needed. Thus, when spray is applied, for example, on any object with the spray nozzle and the container is in a fixed position during at least a period, rotating the container may be omitted should the container be positioned with the peripheral region at the lowest point, so that the gravitation keeps the paint close to the opening of the conduit. Furthermore, it is emphasized that xe2x80x9cthe pressing means are adapted to establish an overpressure of the pressurized medium in the containerxe2x80x9d is to be broadly interpreted and intended to comprise the case in which no real supply of pressurized medium to the container is provided. Rather, for example, the container may initially be filled by so much pressurized medium and pressurized medium of such a high pressure, besides the paint, that this pressurized medium is sufficient for obtaining pressing of all the paint out of the container during a pressure decrease, while maintaining an overpressure in the container when all the paint has been removed.
According to a preferred embodiment of the invention the opening of the conduit is located in the peripheral region at an inner wall of the container, so as to enable discharging of substantially all the paint contained in the container through the opening. A capability of completely emptying the container, with an optimum utilization of the volume thereof, is obtained due to such an arrangement of the opening of the conduit in combination with rotation of the container.
According to another preferred embodiment of the invention the peripheral region extends over a limited part of the extension of the container in a direction substantially in parallel with the axis for the rotation of the container. The opening does not thereby have to be given a disproportionately large extension in this direction so as to achieve an optimum emptying of paint to xe2x80x9cthe very last dropxe2x80x9d.
According to another preferred embodiment of the invention, which constitutes a further development of the embodiment last mentioned, the peripheral region is formed by a valley-like design of the container which is circumferential with respect to the axis of rotation of the container, and having a valley bottom with a maximum distance to the axis of rotation of the container, and wherein the opening is located in the valley bottom. A very well defined point for collection of the paint is obtained in this way, since the extension in the axial direction will be small due to this design, and the paint will move in the valley in a circumferential path and thereby be caught at a point by, or more exactly be pressed out through, the opening.
According to another preferred embodiment of the invention the container is substantially symmetrical with respect to the axis of rotation thereof. Such a design of the container is advantageous, since the paint thereby may be smoothly pressed outwardly towards the periphery of the container by the xe2x80x9ccentrifugalxe2x80x9d force without any substantial formation of swirls or exerting shearing forces on the paint, which may degrade it. At the same time, a capability of even discharging of the paint from of the container is ensured.
According to another preferred embodiment of the invention the pressing means are adapted to press the paint out of the container through compressed air, which in most cases is to be preferred due to the ease of access to this pressurized medium.
According to another preferred embodiment of the invention the pressing means are adapted to supply the pressurized medium to a container in the region of the axis of rotation thereof. This is advantageous since the pressurized medium is then introduced into the space being free from paint at the rotation of the container, which improves the efficiency of the device, as well as because it is easier to fix the means with respect to rotation should this be desired. It also is easier to ensure the capability of removing the container from the means.
According to another preferred embodiment of the invention the device comprises a first valve member arranged in the conduit and a member adapted to control the valve member to open the conduit connection between the container and the spray nozzle when spray application of the paint is to be carried out and, when not, to close the valve member for preventing paint from leaving the container through the conduit. It is thereby ensured that paint is only sprayed out through the spray nozzle when this is really desired. This valve member may be arranged at any location along the conduit and may be located in the spray nozzle itself.
According to another preferred embodiment of the invention the conduit for discharging paint from the container comprises a tube extending from the region of the axis of rotation of the container outwardly towards the periphery of the container to the peripheral region for discharging paint from the container in this region and conducting the paint out of the container substantially along the axis of rotation of the container. By such an arrangement the paint may be efficiently directed out where this is easiest done, while an efficient xe2x80x9cfetchingxe2x80x9d of paint from the container takes place.
According to another preferred embodiment of the invention, which constitutes a further development of the embodiment last mentioned, the device comprises a plurality of conduits extending into the peripheral region for discharging paint from the container at a plurality of locations distributed around the periphery of the container in the direction of rotation thereof. Each of the conduits is formed by a tube. Such a construction may be advantageous by increasing the efficiency of the delivery of paint from the container to the spray nozzle.
According to a further preferred embodiment of the invention the device comprises members for holding the container at a carrier close to the spray nozzle, and the holding members are adapted to hold the container releasably therefrom for removal thereof from the device for replacing it by another container, or filling the container with paint and then inserting it once again in the holding members. By arranging the container in this way, removably from the device, a replacement by a container filled with the same paint color or a container filled with a completely different paint color can occur as soon as the paint in the container in use is running out or a switch to another paint color is to take place. Thus, idle periods of the robot or the machine for spray application may be kept short. It will then be possible to clean and/or fill the container removed in peace and quiet.
Further advantages as well as advantageous features of the invention appear from the following description and the other dependent claims.